Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

1. The capillary tube, as an expansion device, is used in

Water coolers

Room air conditioners

Domestic refrigerators

All of these

2. The freezing point of sulphur dioxide is

-56.6°C

-75.2°C

-135.8°C

-77.7°C

3. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

4. Most thermostatic expansion valves are set for a superheat of

5°C

15°C

20°C

10°C

5. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will never evaporate

Water will evaporate

A gas will never liquefy

6. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Freon

Carbon dioxide

Ammonia

7. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Zero

None of these

Negative

8. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Wet vapour

Saturated liquid

Superheated vapour

9. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Evaporator tubes

Capillary tubes

Refrigerant cooling tubes

10. The boiling point of ammonia is

-30°C

-33.3°C

-10.5°C

-77.7°C

Page 2 of 4

11. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Evaporator and compressor

Compressor and condenser

Receiver and evaporator

12. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

None of the above

Maintains different temperatures in evaporator in proportion to load

13. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

8 bar

2 bar

15 bar

14. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

15. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 3

9: 1

1: 9

16. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

Same

More for small capacity and less for high capacity

17. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Absorber

Condenser

Evaporator

18. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

1.33

4.33

2.33

19. A bootstrap air cooling system has

Four heat exchangers

One heat exchanger

Two heat exchangers

Three heat exchangers

20. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

Page 3 of 4

21. The domestic refrigerator uses following type of compressor

Axial

Centrifugal

Piston type reciprocating

Miniature sealed unit

22. The curved lines on a psychrometric chart indicates

Dew point temperature

Wet bulb temperature

Dry bulb temperature

Relative humidity

23. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Reversed Carnot

Rankine

Carnot

24. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

25. The minimum temperature to which water can be cooled in a cooling tower is

Wet bulb temperature of air

Dry bulb temperature of air

Ambient air temperature

Dew point temperature of air

26. Rating of a domestic refrigerator is of the order of

5 tons

0.1 ton

10 tons

40 tons

27. For obtaining high COP, the pressure range of compressor should be

Low

Any value

Optimum

High

28. Freon group of refrigerants are

Toxic

Inflammable

Non-inflammable and toxic

Nontoxic and non-inflammable

29. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Good electrical conductor

Low boiling point

Large latent heat

30. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Carnot

Ericson

Stirling

Page 4 of 4

31. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

32. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Always less than unity

Any one of the above

Equal to unity

33. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.4

0.376

0.6

34. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

Sub-cooling or under-cooling

Normal cooling

None of these

35. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

36. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

37. Which of the following statement is correct?

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

38. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Above critical temperature

Near critical temperature of refrigerant

Much below critical temperature

39. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

40. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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